Abstract:The molding granule is an intermediate for polymer-bonded explosive （PBX） components. Characterization of the physical parameters of granular system is of great significance to understanding the influence of different granule structure on the performance of PBX components. X-ray computed micro-tomography （XCT） and CT image processing were used to non-destructively characterize physical parameters （including granule diameter， volume fraction， porosity， sphericity and intrinsic density） of the granular random packing systems. The average granule diameter of granular systems is up to 1.04 mm， the volume fraction is up to 68.7%， the lowest porosity is 1.04%， the highest average sphericity is 0.93， and the highest density is 1.44 g·cm^-3. Results show that the type of binder， composition and ratio of explosive crystals， and granulation process have a pronounced influence on the physical parameters of granular packing systems. Moreover， there is a correlation between physical parameters of granular systems. The more dispersed diameter distribution of granular system leads to the larger the average surface area of granules. The larger average granule diameter and lower average sphericity of granular system result in the higher porosity of the granules. The volume fraction of granular systems with larger average granule diameter is higher， and the volume fraction of the granule accumulation is independent of the sphericity when the average sphericity is large. This research provides fundamental insights into understanding the physical parameters and their associations with material properties in molding granular packing systems.

Abstract:The internal crack detection of polymer bonded explosive （PBX） is of great significance and engineering application value for its safety and structural integrity evaluation. In order to improve the imaging detection accuracy and image quality of PBX internal crack defects， the curved surface modified water immersion ultrasonic total focusing imaging method was proposed. On this basis， the delay multiply and sum （DMAS） technology was further combined. The ultrasonic imaging detection of the bottom crack defects of the Φ100.0 mm semi-cylindrical PBX was studied by water immersion method， and high-precision imaging characterization and high signal-to-noise ratio imaging of this bottom crack defect of the curved PBX was realized. The experimental results show that the crack defect height measurement error of the traditional TFM imaging algorithm is 12.0%， and the image signal-to-noise ratio is 1.37 dB. The height measurement error of this crack defect after surface correction is 3.6%， and the image signal-to-noise ratio is 2.13 dB. The crack defect height measurement error of the surface correction algorithm combined with DMAS is only 0.4%， and the image signal-to-noise ratio is 5.32 dB.

Abstract:Atomization performance of free impinging jets with unequal nozzle diameter of 60% Glycerol-water （60G） solution was investigated using PIV technique. The liquid sheet breakup characteristics and droplet behaviors were studied under different Weber numbers （51≤We≤1605）， jet velocities （2.12 m·s^-1≤u≤6.37 m·s^-1） and nozzle diameters （nozzle 1： left nozzle diameter （D₁）=1.5 mm， right nozzle diameter （D₂）=2 mm； nozzle 2： D₁=2 mm， D₂=3 mm）. The droplet distribution of the composite energetic material binder solvent diethylene glycol-water solution was also investigated. The results show that， as We number increases， liquid sheet breakup length increases first and then decreases from edge-free mode （M3） beginning， the liquid sheet thickness and droplet diameter decrease while the droplet velocity increases. Nevertheless， as the nozzle diameter increases， changes in liquid sheet breakup mode are insignificant， and the liquid sheet breakup length， thickness and droplet diameter all increase， while the droplet velocity decreases. At the same time， the empirical correlation equations are obtained between liquid sheet breakup length， liquid sheet thickness， Sauter mean diameter D［3，2］ and nozzle diameter， We number. After validation using the diethylene glycol-water solution， it reveales that with the increase of jet velocity， the droplet diameter decreases and the distribution becomes narrow after the impinging of diethylene glycol-water solution. The error range of D［3，2］ values is within ±15% of the empirical correlation equation， which is consistent with the theoretical prediction results.

Abstract:In order to investigate the combustion characteristics of Al powders in NOx， the reaction mechanism of Al with three nitrogen oxides （NO₂， NO and N₂O） was studied by means of density functional theory ωB97X. Firstly， the geometries of reactants， intermediates， transition states and products were optimized with all parameters. The authenticity of intermediates and transition states was confirmed by frequency analysis. The transition states were further determined by intrinsic reaction coordinates （IRC） calculation， and then the detailed reaction paths and mechanisms were obtained. High precision single-point energy of each structure was obtained by using the double hybrid functional PWPB95 combined with DFT-D3 correction and def2-TZVPP basis set. The rate constants of the related reactions were calculated by using the variational interpolation transition state theory， and the Arrhenius expressions for each reaction are obtained. The results show that the reaction process of Al with NO and NO₂ is that Al and O atoms join together to form the intermediate of the complex， and then break the N─O bond through the ternary ring transition state to form the product. When Al reacts with N₂O， Al reacts with N atoms to form a complex and then the elimination reaction takes place through the ring transition states. The activation energies of the reaction of Al with NO₂， NO and N₂O are 4.3 kJ·mol^-1，249 kJ·mol^-1 and 13.4 kJ·mol^-1， respectively. From 2400 K to 4100 K， the reaction rate of Al with NO₂ and N₂O is higher than 106 m³·mol^-1·s^-1， which indicates that the reaction is easy to take place and the reaction rate is very fast， and the reaction rate of Al with NO is about 1/10000 of that of Al with NO₂ and N₂O.

Abstract:To study the effects of extrusion system nozzle runner structural parameters （cone angle， outlet diameter， and molding section length） on the fluid flow of energy-containing material extrusion process in the direct-in-writing-forming （DIW） technology， an extrusion model of high-viscosity energy-containing materials based on the Polyflow Extrusion module was established， and was verified by extrusion experiments under the working conditions of direct-write 3D printing. The study analyzed the effects of cone angle range （90°-130°）， outlet diameter （0.75-2 mm）， and molding section length （5-20 mm） on the extrusion process of high-viscosity energy-containing materials through the established model. The results show that the Polyflow Extrusion module can accurately simulate the flow behavior of composite energy-containing materials. When the cone angle is 100°， and the nozzle outlet diameter is between 1.5 mm and 1.75 mm， the extrusion process is relatively stable with small extrusion expansion. Additionally， as the length of the molding section grows， the required inlet pressure increases while the outlet expansion effect decreases.

Abstract:The cast TiZrNbV refractory high entropy alloy （RHEA） has high structural strength and good energy release characteristics. As an energetic structural material， it needs to withstand complex dynamic load environments in engineering applications. Studying the spalling behavior of TiZrNbV refractory high entropy alloy and obtaining accurate dynamic constitutive parameters are vital for its engineering application. The spalling characteristics of TiZrNbV RHEA were studied by flat plate impact experiment using a 20mm light gas gun. Parameters such as spalling strength， Hugoniot elastic limit （HEL）， and plastic strain rate were obtained， based on the free surface velocity history. The recycled specimens were analyzed using scanning electron microscopy （SEM）， and the spalling characteristics of TiZrNbV RHEA at different strain rates were analyzed from both macro and micro perspectives. It was shown that the geometrically necessary dislocation of the samples significantly increased with the increase of loading velocity. The spalling strength of TiZrNbV RHEA increases with the loading strain rate and the loading stress， with values ranging from 0.93 GPa to 2.23 GPa. The GTN-JC constitutive model parameters of TiZrNbV RHEA were obtained by calibrating the free surface velocity history of the spallation experiment with a flyer velocity of 580 m·s^-1. The spallation behavior of the sample under 610 m·s^-1 flyer velocity loading was calculated by using the fitted parameters. It was indicated that the free surface velocity curve of the spallation experiment performed well in simulating the spallation behavior of coarse-grained TiZrNbV RHEA. The simulation results show that the free surface velocity curve is consistent before the first tensile stage， which can be used for the dynamic analysis of sample spalling failure. The obtained parameters can provide reference for the engineering application of TiZrNbV RHEA.

Abstract:In order to study the quasi-static compression behavior of polymer bonded explosive （PBX）， the uniaxial quasi-static compression tests were carried out on two typical PBX substitute materials （with and without aluminum powder） at different strain rates， and their mechanical properties were compared and analyzed. Based on the Zu-Wang-Tang （ZWT） model， a new model was proposed to describe the quasi-static compression behavior of materials. The constitutive model parameters were obtained by genetic algorithm， and the model was developed by using Fortran language in the User Material （UMAT） subroutine interface of Abaqus finite element analysis software. Results show that the quasi-static compression process of casting PBX substitute materials can be divided into three stages： elastic compression， stress decay and instability failure. The mechanical behavior of quasi-static compression is obviously correlated with the strain rate. With the increase of the strain rate， the effective compressive strain of the material is basically unchanged， while the logarithms of compression modulus， yield strength and compressive strength are linearly related to the logarithm of strain rate. The addition of aluminum powder can improve the compression modulus， yield strength and compression strength of casting PBX substitute materials. The newly constructed constitutive model can better describe the quasi-static compression behavior of casted PBX substitute materials， and its universality is validated by the finite element analysis software. The coefficients of determination （R²） between the simulated and experimental results are higher than 0.98， indicating a high level of consistency.

Abstract:The explore of energetic molecules faces multiple challenges， and the traditional design method are inefficient. The emergence of computer-aided molecular design has changed the research and development model. This review provides an overview of the development of energetic molecular design and introduces the current research status of computer-aided energetic molecular design. By summarizing the latest advancements in Artificial Intelligence （AI） technology across various design aspects， including performance prediction， molecular generation， retrosynthetic reaction prediction， and reaction condition prediction， we discussed the existing gap between the current approaches in energetic molecular design and other materials design methods. By thinking about the causes of the gap， we present an outlook on the future developmental directions of AI-assisted energetic molecular design. Research indicates that AI has already been applied in property prediction and molecular generation of energetic molecular design， but requires further exploration in retrosynthetic reaction prediction， and reaction conditions prediction. AI-assisted design of energetic molecules holds broad promising application prospects. Data enhancement， transfer learning and high-throughput computing are expected to solve the problem of weak data of energetic molecules. Enhancing AI-assisted prediction of synthesis routes and reaction conditions for energetic molecules shows promise for achieving the automatic molecular design via whole process of “design→evaluation→preparation→verification”. AI-assisted energetic molecular design provides new possibilities for improving the level of energetic molecular design and helps to improve the efficiency of energetic molecule research and development.

Abstract:In order to utilize the performance advantages of carbon nanomaterials， this article summarizes the application of carbon nanomaterials in the desensitizing technology of energetic materials. The effects of typical carbon nanomaterials， such as graphite， carbon nanotubes， graphene and its derivatives， fullerene and its derivatives， on the reduction of impact， shock wave， and friction sensitivity of energetic materials， and explored the desensitization mechanism of different carbon nanomaterials was discussed. Finally， the development prospect of carbon nanomaterials in this field of desensitizing technique of energetic materials is forecasted. It is considered that optimizing the preparation process of carbon nanomaterials and energetic materials， deeply understanding the properties of carbon nanomaterials and conducting functional modification， regulating the interface interaction between carbon nanomaterials and energetic materials and further exploring the desensitization mechanism of carbon nanomaterial will be the focus of future research.

Abstract:The damage behaviors of composite solid propellants were reviewed from four aspects： micro scale， meso scale， macro scale and cross scale. During this process， the observation and characterization methods of damage at different scales， determination methods for damage thresholds， construction methods for damage evolution models， numerical simulation methods for damage， and macro-mesoscopic cross-scale analysis methods were summarized. Based on this， to several shortcomings in current research， the future research directions that need to be further focused on are as follows： expanding the range of influencing factors to be considered in numerical simulation of damage behaviors for composite solid propellants at the microscale， and strengthening the verification of simulation results with experimental research conclusions from multiple aspects； improve the observation ability of damage experiments at the meso scale， the characterization level of damage evolution models， and the computational accuracy of damage numerical simulations； improve the detection accuracy of damage identification testing at the macro scale， the accuracy of determination methods for damage thresholds， and the predictive ability of damage evolution models； further establishing a theoretical method system for cross-scale study of the propellant damage behaviors based on the developed standard specification for the study of damage behaviors for composite solid propellants in single-scale.